Esteban, J., Gradín, C., and Ray, D. (2007). An extension of a measure of polarization with an application to the income distribution of five OECD countries. Journal of Economic Inequalities 5(1): 1-19.

Poggi, A. (2005). Endogenous population subgroups: The best population partition and optimal number of groups. Departament d'Economia Aplicada. Universitat Autònoma de Barcelona ((Document de Treball 05.08)).

Shoven, J.B. (2010). New Age Thinking: Alternative Ways of Measuring Age, their Relationship to Labor Force Participation, Government Policies and GDP. In: Wise, D.A. (ed.). Research Findings in the Economics of Aging. National Bureau of Economic Research: 17-31.